An electric rotating machine has a stator and a rotor. The stator has a stator core around which a stator coil is wound. The rotor is opposed to the stator via an air gap and rotates around a rotational axis. If the electric rotating machine is operated as a motor, an alternating current is transmitted to the stator coil to generate a rotating magnetic field, thereby applying rotating force to the rotor to provide mechanical output. If the electric rotating machine is operated as a generator, rotating force is applied to the rotor from the outside to rotate the rotor, thereby providing electric output generated in the stator coil.
When the electric rotating machine is operated as the motor or the generator to provide the mechanical output or the electric output, respectively, as described above, the stator coil and the stator core produce heat due to losses in the electric rotating machine. An insulation material for the electric rotating machine has an upper limit temperature up to which insulation performance can be kept. When the electric rotating machine is operated, it is necessary to cool the electric rotating machine with the use of any method so as to prevent the insulation material from exceeding the upper limit temperature.
If methods for cooling an electric rotating machine are classified depending on a medium used for cooling, they are divided into a gas cooling method which uses air or hydrogen as a cooling medium and a liquid cooling method which uses cooling water or cooling oil as a cooling medium. Of these the liquid cooling method can be classified into an indirect cooling method and a direct cooling method. In the indirect cooling method, a housing which is provided with a cooling liquid passage on the outside diameter side or inside diameter side of a stator core is installed and the stator core and the stator coil are cooled via the housing. In the direct cooling method, an electrical insulation liquid such as oil is used as a cooling medium and is brought into direct contact with the stator core and the stator coil, which are heat generating portions, for cooling them.
Incidentally, electric rotating machines can be classified into distributed winding and concentrated winding according to the stator coil winding method. Of these the electric rotating machine of the concentrated winding type is configured such that a stator coil is wound via an insulation material around the teeth of the stator core composed of laminated steel plates.
In general, the teeth of a stator core have a rectangle in cross-section; therefore, if a stator coil is wound around the teeth, the bending radius of the coil is increased. Thus, a gap occurs between the teeth and the insulation material or between the insulation material and the coil. This gap is occupied by varnish used to secure the coil or by an air layer. However, since the varnish and air have low thermal conductivity, thermal resistance between the coil and the teeth is increased because of the occurrence of the gap, which degrades cooling performance.
Technologies to solve such a problem are disclosed in e.g. patent documents 1 and 2. Patent document 1 intends to bring a stator coil into close contact with an insulation material by changing the thickness of the insulation material depending on positions to conform the cross-sectional shape of the insulation material to the bending radius of the coil. In patent document 2, the insulation material (the insulation material in the text of patent document 2) is provided with a thin portion and another insulation material is inserted into the thin insulation material portion so as to be held between the coils adjacent to each other. In this way, the coils are intended to be pressed against the thin portions of the insulation materials.